1. Field of the Invention
This invention relates to tied-diaphragm gas pressure regulators. More particularly, it relates to gas pressure regulators having a diaphragm connected to the valve assembly so as to obtain relatively complete valve closure even when particles that may be produced by corrosive gases are present on the valve seat.
2. Description of the Prior Art
There are a number of gas pressure regulators in the prior art which have been developed for use with corrosive compressed gases such as hydrogen chloride and xylene. With corrosive gases, as opposed to non-corrosive gases, corrosion particles tend to deposit within the valve and especially on the valve seat. Some gases tend to generate corrosion particles which collect on the valve seat and interfere with proper shut-off of the valve poppet and thereby the regulation characteristics of the gas pressure regulator. By using a tied diaphragm, a relatively reliable complete valve closure at every shut-off is obtained, whether or not particles are present on the valve seat. This is accomplished by the valve diaphragm moving under pressure so as to pull the valve poppet against the seat.
These prior art tied-diaphragm gas pressure regulators have suffered from a number of problems. One problem is leakage through the diaphragm at the point of connection between the stem attaching the poppet to the diaphragm. In a very common construction, an opening must be made in the diaphragm. The stem is passed through the opening and suitable resilient sealing material such as plastic or rubber is used to attempt to eliminate leakage of gas through the diaphragm around the stem connection. However, these resilient materials are attacked and degraded by corrosive gases. When they are, corrosive gas can pass through the diaphragm into the regulator cap and thence into the ambient surrounds so as to cause a potential hazard. It is also desired to contain other gases such as toxic and high purity gases. A small leak of, for example, a toxic gas can result in a condition hazardous to humans. Beyond this, leakage of costly high purity gas results in unwanted economic loss. Leakage can also result in erratic behavior of the regulator.
Another problem common with prior art tied-diaphragm regulators is that they are sensitive to slight misalignments of the key parts. Slight misalignment of the diaphragm with respect to the valve core assembly causes problems in operation of the regulator. For example, the valve poppet may not close completely due to its being angularly displaced by a misaligned diaphragm to which it is connected by the stem.
One prior art attempt to solve the above-described problems is shown in U.S. Pat. No. 4,257,450. The subject patent describes a gas pressure regulator having a lost-motion connection to the diaphragm. Nevertheless, this construction requires a hole in the diaphragm, which may provide a path for unwanted leakage of corrosive and/or toxic gas. Metal-to-metal and resilient seals are provided in an attempt to cut off this unwanted leakage. As aforementioned, the resilient seals are subject to deterioration through exposure to the corrosive gases. They can even serve as fuel for unwanted combustion in the regulator and a destructive condition commonly known as regulator burnout. Even the metal-to-metal seals may potentially leak.
The subject patent also attempts to solve the misalignment problem by providing a complex mechanism including a number of parts. Both the sealing mechanism and the mechanism to accommodate misalignment are complex and therefore costly to produce.